If cells are essential to life, DNA in the cell nucleus -- the "brains" of the cell -- could be considered essential to the cell. It would seem obvious, then, that DNA is required for proper functioning. What about the nucleus itself? Is such a barrier between DNA and the rest of the cell also critical to the function of life? The answer, it turns out, is a resounding "no"! An entire class of organisms called prokaryotes do not have a separate nucleus within their cells.

Living things on Earth are generally characterized as either prokaryotic or eukaryotic organisms. The difference between the two categories is that prokaryotes have no organelles separated from the rest of the cell by membranes. Prokaryotes, then, can survive just fine without a walled-off nucleus -- their chromosomes simply float free inside the cell. Our cells, on the other hand, are eukaryotic -- extra membranes are necessary for many human cell functions.